Optical arrangements of the aforementioned type are known from practice. For example, beam splitters are used in confocal laser scanning microscopes for separating the detection light that is present as fluorescent light, which carries the information about the sample, from the illumination light that is present as excitation light, with which dyes in the sample are excited. If one positions this beam splitter in the di-/convergent beam path, one has the advantage of a simple optical system and only minor disturbing influences caused by interferences that occur at the beam splitter. What is disadvantageous in comparison to the use of the beam splitter in the collimated beam are the imaging errors that occur in the di-/convergent beam. The imaging errors that are introduced when positioning the beam splitter in the di-/convergent beam are approximately proportional to the thickness of the beam splitter.
In a more recent development in the manufacturing engineering of beam splitters, significantly improved performance in these beam splitters with regard to transmission, reflection, and steepness of the edge has been achieved by the controlled application of considerably more—i.e., up to several hundred—individual coatings. However, these overall thicker layers also lead to higher stress in the coated material. This causes increased deformation in comparison to conventional coating techniques, something that one encounters with thicker substrates.
If such a new and improved beam splitter, with its necessary thickness of approximately 4 mm, is to be used in the di-/convergent beam of a confocal laser scanning microscope, the significant imaging errors introduced as a result of this greater thickness must be corrected for. Up to now this was not necessary with a suitable optical design of the overall system when using conventional beam splitters with a comparatively lesser thickness of for example, 0.75 mm. In conventional optical arrangements it is usual to use plane parallel beam splitters, and to combine these plane parallel beam splitters with other plane parallel glass elements if needed.
For example, a lateral chromatic aberration that has been introduced can be corrected by the use of a second plane parallel glass plate that is tipped 180° in relation to the beam splitter. However, in this case the astigmatism of the system is further increased by correction of the chromatic aberration.
In a further example of a conventional arrangement, the astigmatism that has been introduced is corrected by a further plane parallel glass plate that is rotated meridionally by 90° in relation to the beam splitter. Such correction of the astigmatism, however, further increases the chromatic aberration of the optical arrangement.
Furthermore, it is known when using beam splitters to prevent undesirable interference patterns when used in a collimated beam not to implement them as a plane parallel plate, but as a plate with a slight wedge angle. However, this is described exclusively for use of the beam splitter in a collimated beam. This measure is not needed when using the beam splitter in a di-/convergent beam because the interferences that occur produce a pattern solely through the divergence of light, which does not impair the functionality of the confocal laser scanning microscope. Chromatic aberrations are introduced when using this conventional measure as a result of the wedge angle—the prism effect—, which can be corrected for by using a further identical wedge lamina.